Adhesion and viscosity are two properties which are known to be possessed by all fluids. If you put a drop of water on a metal plate the drop will roll off; however, a certain amount of the water will remain on the plate until it evaporates or is removed by some absorptive means. The metal does not absorb any of the water, but the water adheres to it. The drop of water may change its shape, but until its particles are separated by some external power it remains intact. This tendency of all fluids to resist molecular separation is viscosity.
It is these properties of adhesion and viscosity that cause the “skin friction” that impedes a ship in its progress through the water or an airplane going through the air. All fluids have these qualities.
A meniscus (plural: menisci, from the Greek for “crescent”) is the curve in the upper surface of a standing body of liquid, produced in response to the surface of the container or another object. It can be either convex or concave. A convex meniscus occurs when the molecules have a stronger attraction to each other (cohesion) than to the container (adhesion). This may be seen between mercury and glass in barometers. Conversely, a concave meniscus occurs when the molecules of the liquid attract those of the container. This can be seen between water and an unfilled glass. One can over-fill a glass with water, producing a convex meniscus that rises above the top of the glass, due to surface tension.